Silicone MQ resins or silicone MQ resin/silicone polymer blends containing high levels of an MQ resin are known in the art to be difficult to emulsify by direct emulsification using high shear or by inversion. This invention is directed to a method of emulsifying silicone MQ resin/polydiorganosiloxane blends by employing, what is referred to herein, as an inversion assisting polymer. In particular, the inversion assisting polymer comprises a silicone polymer or a silicone copolymer containing polar functional groups. Some examples of suitable polar functional groups are amino groups, epoxidized amino groups, quaternary ammonium groups, glycidyl groups, mercapto groups, carboxyl groups, polyoxyethylene oxypropylene groups, or combinations thereof. The inversion assisting polymer can be incorporated at levels as low as 4 percent by weight based on the total amount of silicone content. When incorporated, silicone MQ resin/polydiorganosiloxane blends at a resin:polymer ratio of 25:75 to 70:30 can be readily inverted by a mechanism known in the art as catastrophic inversion. This enables oil-in-water (O/W) silicone resin emulsions to be obtained using most conventional nonionic surfactants in a conventional mixer. The method provides aqueous silicone resin emulsions that have been heretofore not been obtainable otherwise.
Water-based delivery of silicone resin materials is desired in many applications. However, the emulsification of silicone resins of the structural type MQ, and blends of MQ silicone resins and silicone polymers, with high levels of MQ resins, i.e., containing 20-90 percent by weight based on the total silicone content, and forming oil-in-water emulsions by conventional means is known to be difficult. For example, while conventional techniques such as direct emulsification using high shear are suitable for low viscosity blends, and emulsification by catastrophic inversion is suitable for high viscosity blends, neither is suitable when MQ resins are present. In particular, the presence of a high level of silicone MQ resins in a silicone resin/silicone polymer blend significantly increases the oil phase viscosity, such that a direct emulsification using high shear fails to yield the particle size most desired for emulsion stability. In addition, the presence of a significant amount of silicone MQ resin also makes the oil phase resistant to inversion, to the extent that often the oil phase remains non-inverted at any water-to-oil ratio.
While mixing a volatile silicone fluid, a volatile organic fluid, or a low molecular weight diluent, with a high silicone resin content oil phase can ease the process of emulsification, such volatile compositions or low molecular weight fluids may not be desired in a given formulation, such that successful emulsification of a silicone MQ resin containing material is limited. In contrast, the present invention provides an effective way of emulsifying materials containing high levels of silicone MQ resins. This is enabled according to the present method by using a small amount of a secondary silicone polymer, referred to herein as the inversion assisting polymer. Its function is to ease the inversion process during emulsification. It has been found that the presence of the inversion assisting polymer does not adversely affect performance of the final formulation. In fact, the inversion assisting polymer can contribute to the final formulation some desirable attributes of its own.
This invention relates to a method of making aqueous silicone resin emulsions containing silicone particles having a particle size in range of 100 nanometer to 5,000 nanometer (0.1 to 5.0 micron). According to the method, the silicone resin emulsions can be obtained by (i) mixing a silicone resin or a blend of a silicone resin and a non-resinous silicone polymer with an inversion assisting polymer, and forming a homogeneous oil phase.
In the second step of the method, (ii) one or more surfactants are mixed with the homogenous oil phase in (i) to form a mixture. By (iii) adding sufficient water to the mixture formed in (ii), inversion of the continuous phase and the dispersed phase is caused to occur resulting in an oil-in-water emulsion. In step (iv), the oil-in-water emulsion formed in (iii) is diluted by the addition of more water; and (v) an oil-in-water emulsion containing silicone particles with sizes in range of 100 nanometer to 5,000 nanometer (0.1 to 5.0 micron) is recovered.
The inversion assisting polymer can be silicon functional or organofunctional. The polysiloxane contains in its molecule at least one functional group. Some representative functional groups include hydroxyl groups, alkoxy groups, amino groups, epoxidized amino groups, glycidyl groups, polyoxyethylene oxypropylene groups, carboxyl groups, mercapto groups, quaternary ammonium groups, or combinations of such groups.
The contribution of the present invention to the state of the art is that it enables those skilled in the art to use inversion processing techniques for making aqueous emulsions containing silicone resins. These and other features of the invention will become apparent from a consideration of the detailed description.
A phase inversion generally occurs when the continuous phase of a dispersion becomes the dispersed phase, or vice versa. Phase inversions in liquid/liquid dispersions are categorized as either catastrophic inversions or transitional inversions. Catastrophic inversions can be caused by simply changing the phase ratio until there is such a high ratio of the dispersed phase that it becomes the continuous phase. In contrast, transitional inversions occur when the affinity of the surfactant for the two phases is altered in order to bring about the inversion. For purposes of the present invention, inversion as used herein is intended to mean a catastrophic inversion.
The acronym MQ as used herein is derived from four symbols M, D, T, and Q, which represent the functionality of structural units present in organosilicon compounds containing siloxane units joined by xe2x89xa1Sixe2x80x94Oxe2x80x94Sixe2x89xa1 bonds. The monofunctional (M) unit represents (CH3)3SiO1/2; the difunctional (D) unit represents (CH3)2SiO2/2; the trifunctional (T) unit represents CH3SiO3/2 and results in the formation of branched linear siloxanes; and the tetrafunctional (Q) unit represents SiO4/2 which results in the formation of crosslinked and resinous compositions. Hence, MQ is used when the siloxane contains all monofunctional M units and tetrafunctional Q units, or a high percentage of M and Q units such as to render it resinous.
The oil phase of the emulsion according to the present invention therefore consists of a blend of a silicone MQ resin and a non-resinous silicone polymer, as well as a small amount of a secondary silicone polymer hereafter referred to as the xe2x80x9cinversion assisting polymerxe2x80x9d.
The silicone resin is a non-linear siloxane resin with a glass transition temperature (Tg ) above 0xc2x0 C. The glass transition temperature is the temperature at which an amorphous material such as a higher polymer changes from a brittle vitreous state to a plastic state. The silicone resin used herein otherwise has the general formula Rxe2x80x2aSiO(4-a)/2 wherein Rxe2x80x2 is a monovalent hydrocarbon group with 1-6 carbon atoms or Rxe2x80x2 can be a functionally substituted hydrocarbon group with 1-6 carbon atoms, and a has an average value of 1-1.8. The resin preferably consists of monovalent trihydrocarbonsiloxy (M) groups Rxe2x80x33SiO1/2 and tetrafunctional (Q) groups SiO4/2, in which Rxe2x80x3 is a monovalent hydrocarbon group having 1-6 carbon atoms. Rxe2x80x3 is most preferably a methyl group. The number ratio of M groups to Q groups is in the range of 0.5:1 to 1.2:1, so as to provide an equivalent wherein a in the formula Rxe2x80x2aSiO(4-a)/2 has an average value of 1.0-1.63. Preferably, the number ratio is 0.6:1 to 0.9:1. If desired, the silicone resin may also contain 1-5 percent by weight of a silicon-bonded hydroxyl radical such as the dimethylhydroxysiloxy (HO)(CH3)2SiO1/2 unit.
The non-resinous silicone polymer can be a linear polysiloxane or a cyclic polysiloxane with a Tg below xe2x88x9220xc2x0 C. It is preferably a polydiorganosiloxane containing hydrocarbon groups having 1-6 carbon atoms or containing functionally substituted hydrocarbon groups having 1-6 carbon atoms. Most preferably, at least 80 percent of the groups should be methyl groups. Polydiorganosiloxanes most preferred are polydimethylsiloxanes terminated with hydroxyl groups or trimethylsiloxy groups. Such polydiorganosiloxanes typically have a viscosity of 0.65-60,000 centistoke (mm2/s). Linear and cyclic polysiloxanes useful herein can be volatile species.
As used herein, the term volatile as the term it applies to silicones, is intended to mean siloxanes having a boiling point less than about 250xc2x0 C. and a viscosity of 0.65-5.0 centistoke (mm2/s). Such compositions typically comprise cyclic alkyl siloxanes of the formula (R2SiO)p or linear alkyl siloxanes of the formula R3SiO(R2SiO)qSiR3 in which R is an alkyl group containing 1-6 carbon atoms, p is 3-6 and q is 0-5. Most preferred are the volatile cyclic methyl siloxanes of the formula {(CH3)2SiO}p and the volatile linear methyl siloxanes of the formula (CH3)3SiO{(CH3)2SiO}qSi(CH3)3 in which p is 3-6 and q is 0-5, respectively.
Some representative examples of linear volatile methyl siloxanes are hexamethyldisiloxane with a boiling point of 100xc2x0 C., viscosity of 0.65 mm2/s, and formula Me3SiOSiMe3; octamethyltrisiloxane with a boiling point of 152xc2x0 C., viscosity of 1.04 mm2/s, and formula Me3SiOMe2SiOSiMe3; decamethyltetrasiloxane with a boiling point of 194xc2x0 C., viscosity of 1.53 mm2/s, and formula Me3SiO(Me2SiO)2SiMe3; dodecamethylpentasiloxane with a boiling point of 229xc2x0 C., viscosity of 2.06 mm2/s, and formula Me3SiO(Me2SiO)3SiMe3; tetradecamethylhexasiloxane with a boiling point of 245xc2x0 C., viscosity of 2.63 mm2/s, and formula Me3SiO(Me2SiO)4SiMe3; and hexadecamethylheptasiloxane with a boiling point of 270xc2x0 C., viscosity of 3.24 mm2/s, and formula Me3SiO(Me2SiO)5SiMe3. Me in these formulas and in formulas which follow represents the methyl group CH3.
Some representative examples of cyclic volatile methyl siloxanes are hexamethylcyclotrisiloxane, a solid at room temperature, with a boiling point of 134xc2x0 C. and formula (Me2SiO)3; octamethylcyclotetrasiloxane with a boiling point of 176xc2x0 C., viscosity of 2.3 mm2/s, and formula (Me2SiO)4; decamethylcyclopentasiloxane with a boiling point of 210xc2x0 C., viscosity of 3.87 mm2/s, and formula (Me2SiO)5; and
dodecamethylcyclohexasiloxane with a boiling point of 245xc2x0 C., viscosity of 6.62 mm2/s, and formula (Me2SiO)6.
The ratio of the silicone resin to the non-resinous silicone polymer in the blend is 5:95 to 95:5 by weight, preferably 20:80 to 70:30, and most preferably 30:70 to 70:30. The blend of the silicone resin and non-resinous silicone polymer can be obtained either by (i) directly mixing the silicone resin and non-resinous silicone polymer to form a homogenous mixture in the form of a clear solution, or by (ii) mixing an organic solvent solution of the silicone resin and the non-resinous silicone polymer, and then stripping the organic solvent by vacuum distillation at an elevated temperature.
Blends of the silicone resin and the non-resinous silicone polymer can be delivered in the form of silicone pressure sensitive adhesive if desired. Such compositions can be prepared by mixing a silanol-terminated polydiorganosiloxane having a Tg below xe2x88x9220xc2x0 C., with a silanol-containing silicone resin having a Tg above 0xc2x0 C., and lightly cross-linking the mixture by condensation of the silanol groups in the polydiorganosiloxane with the silanol groups in the silicone resin. Such silicone pressure sensitive adhesives include (i) 20-80 parts by weight, preferably 30-60 parts, of the silanol-terminated polydiorganosiloxane with a Tg below xe2x88x9220xc2x0 C., and (ii) 20-80 parts by weight, preferably 40-70 parts, of the silanol-containing silicone resin with a Tg above 0xc2x0 C.
Particularly preferred silicone pressure sensitive adhesive compositions can be prepared by mixing (i) 30-60 parts by weight of the silanol-terminated polydiorganosiloxane with a Tg below xe2x88x9220xc2x0 C. and a viscosity of 0.1-30000 Pa.s at 25xc2x0 C., with (ii) 40-70 parts by weight of the silanol-containing silicone resin with a Tg above 0xc2x0 C. The silanol-containing silicone resin should include monovalent trihydrocarbonsiloxy (M) groups of the formula Rxe2x80x33SiO1/2 and tetrafunctional (Q) groups of the formula SiO4/2, in which Rxe2x80x3 is a monovalent hydrocarbon group having 1-6 carbon atoms, and the number ratio of M groups to Q groups is in the range 0.5:1 to 1.2:1. Suitable silicone pressure sensitive adhesive compositions can be made in accordance with the method described in U.S. Pat. No. 5,319,120 (Jun. 7, 1994).
In an alternate and similar embodiment, the blend of the silicone resin and the non-resinous silicone polymer can be delivered in the form of a mixture of a silicone pressure sensitive adhesive as noted above, and an additional linear or cyclic polysiloxane having a glass transition temperature below xe2x88x9220xc2x0 C. In this alternate embodiment, the additional polysiloxane most suitable is a polydiorganosiloxane containing hydrocarbon groups having 1-6 carbon atoms or functionally substituted hydrocarbon groups having 1-6 carbon atoms, and a viscosity of 0.65-60,000 centistoke (mm2/s). The ratio of the silicone resin to the total non-resinous silicone polymer in composition of the mixture containing the silicone pressure sensitive adhesive and the additional linear or cyclic polysiloxane should be 5:95 to 95:5 by weight, preferably 20:80 to 70:30 by weight, and most preferably 30:70 to 70:30 by weight.
The inversion assisting polymer which is used according to the this invention is a silicon functional polysiloxane or an organofunctional polysiloxane. By silicon functional is meant that the functional group is directly attached to a silicon atom. By organofunctional is meant that the functional group is attached to a silicon atom generally via divalent radicals such as alkylene groups. Suitable inversion assisting polysiloxanes generally have the formula:Rxe2x80x3xe2x80x3aRxe2x80x23-aSiO(Rxe2x80x22SiO)x(Rxe2x80x2Rxe2x80x3SiO)y(Rxe2x80x2Rxe2x80x2xe2x80x3SiO)zSiRxe2x80x23-aRxe2x80x3xe2x80x3a wherein Rxe2x80x2 represents the same or a different monovalent hydrocarbon groups having 1-6 carbon atoms; Rxe2x80x3, Rxe2x80x2xe2x80x3 and Rxe2x80x3xe2x80x3 each represent the same or a different silicon functional group or an organofunctional group such as an hydroxyl group, an alkoxy group, an amino group, an epoxidized amino group, a glycidyl group, a polyoxyethylene oxypropylene group, a carboxyl group, a mercapto group, a quaternary ammonium group, or combinations of such groups. The group can be either directly linked to a silicon atom or linked to a silicon atom via a divalent alkylene linking radical. In the formula, a is 0 or 1, and the ratio of x to (y+z) is 99.5:0.5 to 90:10.
Some particular examples of suitable organofunctional groups which can be included in the inversion assisting polymer arc hydroxyl groups such as xe2x89xa1SiOH or xe2x89xa1SiCH2CH2CH2OH, alkoxy groups such as xe2x89xa1SiOC2H5 or xe2x89xa1SiCH2CH2CH2OC2H5, amino groups such as xe2x89xa1SiCH2CH2CH2NH2, epoxidized amino groups such as xe2x89xa1SiC4H8NRC2H4NR2 where R is about 20 percent hydrogen and about 80 percent of the group xe2x80x94CH2CH2CH(OH)CH2OH; glycidyl groups such as xe2x89xa1Si(CH2)3OCH2CH(O)CH2, polyoxyethylene oxypropylene groups such as xe2x89xa1Si(CH2)3(OCH2CH2)3[OCH2(CH3)CH]3OH, carboxyl groups such as xe2x89xa1Si(CH2)3 COOH, mercapto groups such as xe2x89xa1Si(CH2)3SH, and quatemary ammonium groups such as xe2x89xa1SiC4H8NHC2H4NHCH2CH(OH)CH2N+(CH3)3CIxe2x88x92.
If desired, the inversion assisting polymer can be used as a mixture containing (i) a functional polydiorganosiloxane; with (ii) another silicone fluid with a lower molecular weight; and/or (iii) an organic compound such as a long chain alcohol. The mixture should be such as to have a ratio in which functional polydiorgansiloxane (i) is at least 70 percent by weight of the mixture.
An initial step in preparing emulsions according to the invention is to mix (i) the blend of the silicone resin and the non-resinous silicone polymer with (ii) the inversion assisting polymer, to form the oil phase of an emulsion. The oil phase should be prepared such that it includes 1-50 percent by weight, preferably 3-20 percent by weight, and most preferably 5-10 percent by weight of the inversion assisting polymer. The oil phase should also include 50-99 percent by weight, preferably 80-97 percent by weight, and most preferably 90-95 percent by weight of the blend of the silicone resin and the non-resinous silicone polymer. In preparing the oil phase, the blend of silicone resin and non-resinous silicone polymer should be mixed homogeneously with the inversion assisting polymer.
Emulsions according to this invention can be prepared using organic surfactant. The surfactants may be anionic surfactants, cationic surfactants, nonionic surfactants, amphoteric surfactants, or surfactant mixtures, Nonionic organic surfactants and anionic organic surfactants are especially preferred as mixtures containing an anionic and a nonionic surfactant, or as a mixtures containing two nonionic surfactants. In the latter case, one nonionic surfactant should have a low Hydrophile-Lipophile Balance (HLB) while the other nonionic surfactant has a high HLB, such that the two nonionic surfactants have a combined HLB of 11-15, preferably 12.5-14.5. The effectiveness of the method of the present invention is most distinctive when nonionic surfactants are employed.
Representative of suitable anionic organic surfactants which can be used include alkali metal soaps of higher fatty acids, alkylaryl sulphonates such as sodium dodecyl benzene sulphonate, long chain fatty alcohol sulphates, olefin sulphates and olefin sulphonates, sulphated monoglycerides, sulphated esters, sulphonated ethoxylated alcohols, sulphosuccinates, alkane sulphonates, phosphate esters, alkyl isethionates, alkyl taurates, and alkyl sarcosinates. Some suitable cationic organic surfactants include alkylamine salts, quaternary ammonium salts, sulphonium salts, and phosphonium salts. Some suitable nonionic surfactants include siloxane polyoxyalkylene copolymers, the condensates of ethylene oxide with long chain fatty alcohols or fatty acids such as a C12-16 alcohol, the condensates of ethylene oxide with an amine or an amide, the condensation products of ethylene and propylene oxide, esters of glycerol, sucrose, sorbitol, fatty acid alkylol amides, sucrose esters, fluoro-surfactants, and fatty amine oxides. Some suitable amphoteric organic surfactants include imidazoline compounds, alkylaminoacid salts, and betaines.
Some commercially available nonionic surfactants most suitable according to the present invention include polyoxyethylene fatty alcohols sold under the tradename BRIJ by Uniqema (ICI Surfactants), Wilmington, Del. One example of this type of nonionic surfactant is BRIJ 35 Liquid, an ethoxylated alcohol also known as polyoxyethylene (23) lauryl ether. BRIJ 30 is another ethoxylated alcohol also known as polyoxyethylene (4) lauryl ether. Some additional and most suitable nonionic surfactants include the ethoxylated alcohols sold under the trademark TERGITOL(copyright) by The Dow Chemical Company, Midland, Mich. Some example include TERGITOL(copyright) TMN-6 which is an ethoxylated alcohol also known as ethoxylated trimethylnonanol, and TERGITOL(copyright) 15S15 which is an ethoxylated alcohol also known as C12-C14 secondary alcohol ethoxylate.
The method of making silicone resin emulsions according to the invention is carried out by adding the surfactant(s) to the oil phase containing the silicones, and agitating the oil phase with a conventional mixer. Water is then added to the oil phase containing the surfactant(s) in a stepwise fashion, such that catastrophic inversion occurs, and an oil-in-water emulsion is formed. It is also possible according to another embodiment for one or more of the surfactant(s) to be first dissolved or dispersed in water, and then the resulting aqueous solution or dispersion is added to the oil phase, which contains the same surfactant, a different surfactant, or no surfactant. In this instance, the amount of water used in the aqueous surfactant solution or dispersion for addition to the oil phase is such that it comprises a minimum or a slight excess of the minimum amount of water necessary to cause inversion. Typically, the amount of water required will be about 2-20 percent by weight of the oil phase. Moderate to high shear in a conventional mixer may be required to induce the inversion, however. The emulsion is then diluted with more water, or added with other additives such as biocides, thickeners, and freeze-thaw stabilizer, to form the final composition. The particle diameter of the silicones in such emulsions will typically be in a range of about 100-5,000 nanometer (0.1 to 5.0 micron), depending on the amount of surfactants and inversion assisting polymer used in the preparation.
Silicone resin emulsions according to the invention are capable of delivering performance properties such as controlled tack, lubrication, and assist in film formation. Thus, they can be used in coating applications, and in household, cosmetic and personal care applications, to provide greater durability, protective qualities, water resistance, and barrier properties. In some applications, it may be necessary to avoid the use of hydrocarbon-based solvents in delivering the silicone resin however.